# Chapter 2: Noise and Vibration

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Chapter 2: Noise and Vibration
| School of Environmental Engineering EAT 342: Noise Pollution Control Chapter 2: Noise and Vibration By: Dr. Sara Yasina Yusuf 1

Course Objectives & Learning Objectives
This chapter reflects CO2: Ability of defining the properties of sound, quantifying the noise levels and decibel as well as to characterize the noise. Learning Objectives for the chapter: LO-1: Able to SKETCH pure tone wave and DEFINE the properties of sound waves (i.e. Frequency, amplitude, wavelength and period). CALCULATE the speed of sound, sound pressure, frequency and wavelength. LO-2: DEFINE sound scale in decibel. LO-3: DIFFERENTIATE and CALCULATE the Sound Power Level, Sound Intensity and Sound Pressure Level. LO-4: CALCULATE the Sound Pressure/Power Level, summation of sound pressure using formula, table and graph, substraction and averaging of Sound Pressure/Power Level LO-5: DISCUSS and ANALYZE noise characteristics, such as weighting networks, octave bands and rating systems LO-6: DISCUSS the techniques in measuring community/environmental noises. COLLECT and ASSESS the Leq as well as Ldn measured through the PBL assignment. LO-7: DISCUSS various types of community noise sources and its criteria. COMPARE the measured data obtained via PBL and CRITIC on the levels to protect human health and welfare

Content The basic physics of sound Noise measurement
Sound and types of sound Speed of sound Community Noise Sources and Criteria Sound pressure Properties of Sound Waves Transportation noise Frequency Other internal combustion engines Wavelength Construction noise Zoning and siting considerations Characteristics of noise and Desibel scale Levels to protect Health and Welfare Frequency and Loudness Sound level and decibel scale Weighting networks Octave bands Rating systems

The basic physics of sound – Sound & Types of Sound
What is sound wave? A sound wave is an air pressure disturbance that results from vibration that propagates through an elastic medium (air, water, etc.) at a speed characteristic of that medium. Patterns of noise: Steady-state or continuous Intermittent Impulse or impact

The basic physics of sound – Sound & Types of Sound
Continuous noise is an uninterrupted sound level that varies less than 5 dB during the period of observation Intermittent noise is a continuous noise that persists for more than 1 second that is interrupted for more than 1 second Impulse noise is a change of sound pressure of 40 dB or more within 0.5 second with a duration of less than 1 second  high pitch or intensity, lifetime of less than 1 sec.

The basic physics of sound - Sound & Types of Sound
Behaviour of sound waves Reflection Waves bounce off a surface Echoes & reverberation Refraction Waves bend when they pass through a boundary Diffraction Waves spread out when they pass through a small gap Interference 2 waves superpose to form a resultant wave of greater or lower amplitude

The basic physics of sound – Sound & Types of Sound
Reflection Interference

The basic physics of sound – Sound & Types of Sound
Example 2.0 A fishing boat received the echo 50 ms after sending it. The speed of sound in water is 1500 m/s Determine the depth of the water.

The basic physics of sound – Speed of Sound
In a free field, sound propagates with the velocity c defined by For the velocity of sound in air sufficiently accurate at normal temperatures, 0–30oC Eqn. 2.1 Eqn. 2.2 where TK and TR are the temperature in Kelvin and Rankine, respectively Eqn. 2.3 where TC is the temperature in centigrade 0F=R - 459

The basic physics of sound – Speed of Sound
Example 2.1 Determine the speed of sound at 20oC (68oF) in both metric (m/s) and English (ft/s) units. 0F=R - 459

The basic physics of sound – Sound Pressure
For a pure tone, the sound pressure p can be described as where a is the amplitude in Pascals, ω is the angular frequency in radians per second, t is the time in seconds, and f is the frequency in hertz. Eqn. 2.4 Eqn. 2.5 A pure tone is a tone with a sinusoidal waveform, i.e. a sine or cosine wave

The basic physics of sound – Sound Pressure
Figure 2.1, and 2.2 show the pure tone oscillation, although pure tones do not often exist in nature. The field of acoustics and noise control has nearly uniformly adopted the metric system throughout and, as such, the unit used for measuring sound pressure is the Pascal(Pa).

The basic physics of sound – Properties of Sound Waves
Figure 2.1 : Pure tone

The basic physics of sound – Properties of Sound Waves
Figure 2.2: Pure tone from a tuning fork

The basic physics of sound – Properties of Sound Waves
The frequency of a sound indicates the number of cycles performed in 1 s: where T is the period of one full cycle. The unit for frequency is the hertz (Hz): A high frequency pure tone is perceived to have a high pitch.  The audible frequency range to humans is 20–20,000 Hz Above 20,000 Hz is ultrasonic. Below 20 Hz is sometimes called infrasonic. Eqn. 2.6

The basic physics of sound – Properties of Sound Waves
Figure 2.3 : Frequency and amplitude

The basic physics of sound – Properties of Sound Waves

The basic physics of sound – Properties of Sound Waves
The wavelength λ is equal to the distance the oscillations have propagated in the time period T: This shows that the wavelength is inversely proportional to the frequency. In the audio frequency range, the low frequencies have wavelengths of several meters (or feet), whereas the wavelengths for the high frequencies are only a few centimeters (or fractions of an inch). Eqn. 2.7

The basic physics of sound – Properties of Sound Waves
Figure 2.5 : Harmonic oscillation of pressure

Characteristics of Noise – Frequency and Loudness
There are two important characteristics of sound or noise - frequency and loudness. The number of pressure variations per second is called the frequency of sound, and is measured in Hertz (Hz) which is defined as cycles per second. The higher the frequency, the more high-pitched a sound is perceived. Frequency  Pitch Amplitude  Loudness No oscillations?

Characteristics of Noise – Frequency and Loudness
Example 2.2 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units.

Characteristics of Noise – Frequency and Loudness
The curves in Figure 2.6 indicates the loudness – the subjective interpretation of the magnitude of sound – for pure tones. The loudness of a sound depends on the wave's amplitude. The louder the sound, the higher the amplitude. So, amplitude is also a way of measuring the energy has. The higher the energy, the higher the amplitude resulting a louder sound.

Characteristics of Noise – Frequency and Loudness
20Hz Figure 2.6 : Normal equal loudness contours for pure tones.

Characteristics of Noise – Frequency and Loudness
For example, as can be seen in Fig. 2.6, the threshold of hearing at Hz is about 4 dB (5 x 10-5 Pa). A 20-Hz tone must have a sound pressure level about 70 dB higher than a tone at 1000 Hz in order for a person just to hear the tone. The curves also indicated the loudness—the subjective interpretation of the magnitude of sound—for pure tones. The units describing loudness are called phons. By definition, the phon is equal to the sound pressure level (in dB) reference to 20 μPa of an equally loud 1000-Hz tone. Pain will occur when the loudness exceeds 120 phons.

Characteristics of Noise – Sound Level and Decibel Scale
As explained previously, sound is measured in unit of pressure and normally referred in Pascal and Newton per meter square or “psi”. The lowest audible sound pressure is Pa (or 20x10-6 Pa equivalent 20 μPa). This value is very low as compared to sound emitted from a taking off jet i.e., 200 Pa. Note that the range of difference between these is so great. Therefore, a scale based on the logarithm of the ratios of the measured quantities is used. Measurements on this scale are called levels.

Characteristics of Noise – Sound Level and Decibel Scale
rms Sound Pressure Physically, the rms value is indicative of the energy density of the disturbance. Mathematically, the rms value is obtained by squaring the sound pressures at any instant of time and then integrating over the sample time and averaging the results. The rms value is then the square root of this time average: Where the overbar refers to the time-weighted average and T is the time period of the measurement Eqn. 2.8

Characteristics of Noise – Sound Level and Decibel Scale
Sound Power Travelling waves of sound pressure transmit energy in the direction of propagation of waves  magnitude of the displacement times component of force in the direction of the displacement The rate at which this work is done Sound Power Level is defined as : Where, Lw = Sound Power level in dB W = Sound Power in watt Wo = Reference sound power = watt The standard reference power watt is the threshold power of our hearing. = WORK = (SOUND) POWER, Watt Eqn. 2.9

Characteristics of Noise – Sound Level and Decibel Scale
Please note that, direct reading of sound power is not possible. Sound Level meter functions by measuring sound pressure or the difference in pressure due to vibration of air molecule, compared to 1 atm. Equation 2.2 describes the power emitted from a noise source. For example, when we speak, our voice vibrates the air molecule causing the pressure to increase and a sound power is generated. What is measured by the instrument is the pressure. Development of sound measurement instruments are currently based on the measurement of pressure and not the power.

Characteristics of Noise – Sound Level and Decibel Scale
Example 2.3 Given Lw = 90 dB. What is the sound power in watt? Wo = Reference sound power = watt Eqn. 2.10

Characteristics of Noise – Sound Level and Decibel Scale
Sound Intensity Sound intensity (I) is defined as the time-weighted average sound power per unit area normal to the direction of propagation of the sound wave I = Sound Intensity (watt/m2) W = Sound Power (watt) A = area (sphere) normal to source (m2) = 4πr2, r is distance from source The higher the area, the lower will be the sound heard at a distance from origin. Therefore, sound intensity is reduced proportionately with increase in coverage area. Eqn. 2.11

Characteristics of Noise – Sound Level and Decibel Scale
Intensity is related to sound pressure in the following manner: Where, I = Intensity (watt/m2) prms = root mean square pressure, Pa ρ = density of medium (kg/m3) c = speed of sound in medium (m/s) Eqn. 2.12

Characteristics of Noise – Sound Level and Decibel Scale
Both the density of air and speed of sound are a function of temperature. Given the temperature and the pressure, the density of air may be determined from Standard Table. Sound Intensity Level can be written as: Where, LI = Sound Intensity Level (dB) I = Sound Intensity (watt/m2) Eqn. 2.13

Characteristics of Noise – Sound Level and Decibel Scale
Example 2.4 Given that a sound power in watt from a pile driver in a construction site is 1x10-3 watt. Determine the sound intensity at the perimeter which will be heard by the following two cases: i) Heidi stands at a distance 15 meter from source ii) A hawker stands at a distance 50 meter from source Sound Intensity level? A = 4πr2, r is distance from source

Characteristics of Noise – Sound Level and Decibel Scale
Sound Pressure Level In order to cope with the problem of an ‘astronomical’ range of numbers of the sound pressure level (i.e; normal healthy level of Pa vs. Saturn rocket at liftoff of >200 Pa), a scale based on the logarithm is introduced as “levels” The unit for these types of measurement scales is the Bel, named after Alexander Graham Bell: L’ = levels, Bel Q = measured quantity Q0 = reference quantity L’ = log10 (Q/Qo) unit: Bel Eqn. 2.14

Characteristics of Noise – Sound Level and Decibel Scale
The sound pressure level then is a logarithmic ratio Lp defined as: where prms = the sound pressure of interest (in Pa) and pref = reference sound pressure (in Pa) usually chosen as the limit of hearing of 20 μPa. NOTE: (P log10 xn) = P (n) log10 x The unit for the sound pressure level, SPL or Lp, is the decibel (dB) Eqn. 2.15

Characteristics of Noise – Sound Level and Decibel Scale
The LP is measured against a standard reference pressure, pref = po = 2 x 10-5 N/m2 which is equivalent to zero decibels. The relationship between sound pressure and sound pressure level (with 20 μPa as the reference sound pressure) is shown in Table A scale showing some common sound pressure level is shown in Figure 2.7.

Characteristics of Noise – Sound Level and Decibel Scale
Table 2.1

Characteristics of Noise – Sound Level and Decibel Scale
Figure 2.7: Relative scales of sound pressure levels

Characteristics of Noise – Sound Level and Decibel Scale
Example 2.5 Determine the sound pressure level for sound pressures of p = 1 Pa and p = 1 atm (1.013 × 105 Pa) (reference to 20 μPa)

Characteristics of Noise – Sound Level and Decibel Scale
Combining Sound Pressure Levels Since we’re dealing with the logarithmic heritage in SPL, adding the decibels is the same as multiplying them. For example, adding 0dB (20µPa) noise with 0dB to it, you’ll get a dB noise. Two approaches: 1) addition through formula, 2) addition through graphical solution

Characteristics of Noise – Sound Level and Decibel Scale
For skeptics, this can be demonstrated by converting the dB to SPL, adding them and converting back to dB. Thus, the addition of these Sound Pressure Level is denoted by: Lp = 20 log10 (P/Po) dB Eqn. 2.16 Lpt = 10 log10 [ Σ (10)Lpi/10 ] dB Eqn. 2.17

Characteristics of Noise – Sound Level and Decibel Scale
The addition of these Sound Power Level is denoted by: Lw = 10 log10 (w/wo) dB Eqn. 2.18 Lwt = 10 log10 [ Σ 10(Lwi/10) ] dB Eqn. 2.19

Characteristics of Noise – Sound Level and Decibel Scale
A graphical solution for this type of problem is provided as in Figure For noise pollution work, results should be reported to the nearest whole number.

Characteristics of Noise – Sound Level and Decibel Scale
For equal decibel values, a shortcut method can be applied: n 10 log10 (n) 1 0.00 6 7.78 2 3.01 7 8.45 3 4.77 8 9.03 4 6.02 9 9.54 5 6.99 10 10.00

Characteristics of Noise – Sound Level and Decibel Scale
Figure 2.8: Graph for solving decibel addition problems

Characteristics of Noise – Sound Level and Decibel Scale
Example 2.6 Three SPL’s 68 db, 79 dB and 75 dB, what is SPL of combination? 68 dB 75 dB = 7 75.8 dB 80.7dB 79 dB = 3.2

Characteristics of Noise – Sound Level and Decibel Scale
Alternatively, this can be solved by converting the readings to SPL, adding them and convert back to SPL:

Characteristics of Noise – Sound Level and Decibel Scale
Calculate the final sound power level that would be heard for noise levels 92, 98, 100, 95 and 85 dB using: Formula Graph

Characteristics of Noise – Sound Level and Decibel Scale
Averaging Sound Average sound can be calculated as the same as the calculation of summation of sound. As sound is referred in form of log, so the average requires calculation in form of pressure and power. The pressure is then calculated, averaged and finally antilog.

Characteristics of Noise – Sound Level and Decibel Scale
Average Sound Pressure Level is given as: Where, = Average Sound Pressure Level at reference pressure 20 μPa, dB (A) N = Number of sample Lj = Sound Pressure level measured at reference pressure 20 μPa, dB(A) j = 1,2,3…n Eqn (a)

Characteristics of Noise – Sound Level and Decibel Scale
The latter equation is only applicable to sound levels in dBA It may also be used to compute average sound power levels if the factors of 20 are replaced with 10 s Where, = Average Sound Pressure Level at reference pressure 20 μPa, dB (A) N = Number of sample Lj = Sound power level measured at reference power level W, dB(A) j = 1,2,3…n Eqn (b)

Characteristics of Noise – Sound Level and Decibel Scale
Example 2.7 Average the Sound Pressure Level for following field monitoring data, 51, 38, 78 and 68 dB(A). Eqn (a)

Characteristics of Noise – Weighting Networks
Weighting networks are used to account for the frequency of a sound. They are electronic filtering circuits built into the sound level meter to attenuate certain frequencies – with a prejudice something like that of the human ear. Normally, there are 3 weighting characteristics: A, B and C The very low frequencies are filtered quite severely by the A network, in a manner similar to the response of the ear, but only moderately by the B network and hardly at all by the C network.  Therefore, if the measured sound level on the C network is much higher than that on the A network, much of the sound energy is concentrated in the low frequency region.

Characteristics of Noise – Weighting Networks
“A” Scale Filters out low frequencies Response curve is similar to sensitivity of human ear “C” Scale Filters out very little (only the extreme low frequencies) If a measurement is higher on the C scale than the A scale, the noise has a low frequency component Used to estimate the effectiveness of ear protectors A specialized filter, the "D" weighting, has also been introduced for aircraft noise measurements. Figure 2.9 shows the response characteristics of the three basic networks as prescribed by the American National Standards Institute (ANSI) spec. no. S1.4 – 1971.

Characteristics of Noise – Weighting Networks
Figure 2.9: Frequency Response Characteristics of Various Weighting Networks

Characteristics of Noise – Weighting Networks
When a weighting network is used, the sound level meter is electronically subtracts or adds the number of dB shown at each frequency shown in Table 2.2 Readings taken when a network is in use are said to be “sound levels” rather than “sound pressure levels”. The readings taken are designated in decibels in one of the following forms: dB(A), dBa, dBA; dB(B), dBb, dBB; dB(C), dBc, dBC. Tabular notations may refer to LA , LB , LC

Characteristics of Noise – Weighting Networks
Table 2.2: Sound Level Meter network weighting values - CFA

Characteristics of Noise – Weighting Networks
Example 2.8 A new type 2 sound level meter is to be tested with two pure tone sources that emit 90 dB. The two sources are at 1,000 Hz and Hz. Estimate the expected readings on the A, B and C weighting networks.

Characteristics of Noise – Weighting Networks
Example 2.9 The following sound levels were measured on the A, B, and C weighting networks: Source 1: 94 dB(A), 95 dB(B) and 96 dB(C) Source 2: 74 dB(A), 83 dB(B) and 90 dB(C) Characterize the sources as “low frequency” or “mid/high frequency”.

Characteristics of Noise – Weighting Networks
Added Problem The measured octave band sound pressure levels around a punch press is given in table below. Determine the A-weighted sound level and the overall sound pressure level. Octave band center frequency, Hz 31.5 63 125 250 500 1000 2000 4000 8000 LP (dB) 70 81 89 101 103 93 83 77 74 CFA, dB LP + CFA (dBA)

Characteristics of Noise – Octave Bands
The human ear is sensitive to sound in the frequency range from approximately 16 Hz to 16 kHz. Impractical to measure the sound pressure level at each frequency in this range The measurements are made over an interval of frequency which is called the bandwidth and is specified by an upper and lower frequency limit fi+1 and fi are called cut-off frequencies. In acoustics the frequency bandwidths are usually specified in terms of octaves and one-third-octaves Normally, considering an 8 to 11 octave bands

Characteristics of Noise – Octave Bands
An octave is defined as an interval of frequency such that the upper frequency limit is twice the lower limit, that is: For the 1/3-octave bands, it is defined as: The center frequency of the band is defined as the geometric mean of the upper and lower frequencies for the interval: Relationship of center frequency for an octave? For 1/3 octave?

Characteristics of Noise – Octave Bands
Generation law for octave and third octave bands Octave band − oct. filter 1/3 Octave band − third oct. filter

Characteristics of Noise – Octave Bands
Table 2.3: Octave bands

Characteristics of Noise – Octave Bands
Added Problem Find the geometric mean frequency for 1:1 octave and 1:3 octave bands for the following band no. Octave Band 1/3 Octave Band Lower Center Upper Frequency f1 (Hz) f0 (Hz) f2 (Hz)  22  44  88  177

Characteristics of Noise – Octave Bands
Figure 2.10: (a) One-third octave band analysis of a small electric motor. (b) Narrowband of analysis of a small electric motor

Characteristics of Noise – Octave Bands
Noise level measured with 1:1 Octave Band Filters

Characteristics of Noise – Octave Bands
Noise level measured with 1:3 Octave Band Filters

Characteristics of Noise – Rating Systems
Goals of Noise-Rating System An ideal noise-rating system is one that allows measurements by sound level meters or analyzers to be summarized succinctly and yet represent noise exposure in a meaningful way Our response to sound is strongly dependent on the frequency of the sound Significant factors in annoyance: type of noise & time of day that it occurred Ideal system: a) frequency, b) daytime or nighttime noise, c) capable of describing the cumulative noise exposure.

Characteristics of Noise – Rating Systems
The LN Concept LN is a statistical measure that indicates how frequently a particular sound level is exceeded. Example: if L30 = 67 dB, means that 67 dB(A) was exceeded for 30% of the measuring time. A plot of against N (where N = 1%, 2%, 3%,….) look like the cumulative distribution curve (Figure 2.11) Allied to the cumulative distribution curve is the probability distribution curve (Figure 2.12) – showing how often the noise levels fall into certain class intervals.

Characteristics of Noise – Rating Systems
Figure 2.11: Cumulative distribution curve

Characteristics of Noise – Rating Systems
Frequency of occurrence, % Calculation of L30 = 67 dB: Where; N = the sum of the percentages L = lower limit of the left-most class interval added Eqn. 2.21 Figure 2.12: Probability distribution plot

Characteristics of Noise – Rating Systems
The Leq Concept The equivalent continuous equal energy level (Leq) can be applied to any fluctuating noise level. It is expressed as: Eqn. 2.22

Characteristics of Noise – Rating Systems
Added Problem Refer to the attachment distributed in the class. Construct a cumulative distribution curve (Sound level vs. Percentage time greater than stated value) Find: Lmax L90 Lmin Leq L1 L50

Characteristics of Noise – Rating Systems
Example 2.10 Consider the case where a noise level of 90 dBA exists for 10 minutes and is followed by a reduced noise level of 70 dBA for 30 minutes. What is the equivalent continuous equal energy level for the 40-minute period? Assume a five-minutes sampling interval.

Characteristics of Noise – Rating Systems
The Ldn Concept Ldn is the Leq computed over a 24-hr period with a “penalty “ of 10 dBA for a designated night time period. Day-night average – subscript “dn” In airport noise applications, Ldn is referred to LDN Night time period  10 pm to 7 am Ldn equation is derived from the Leq equation with the time increment specified as 1 s (1  86, 400 seconds)

Characteristics of Noise – Rating Systems
So, eqn becomes: 10 log [1/86400] ≈ 49.4, the day-night average sound level: Eqn. 2.23 Eqn. 2.24

Characteristics of Noise – Rating Systems
Time (h) Sound Level (dBA) 0000 – 0500 52 0500 – 0700 78 0700 – 1130 90 1130 – 1200 70 1200 – 1530 1530 – 1800 1800 – 2200 60 2200 – 0000 Example 2.11 The USEPA estimated that, in 1974, the following was a typical noise exposure pattern for a factory worker living in an urban area. Estimate the Ldn for the exposure shown.

Content The basic physics of sound Noise measurement
Sound and types of sound Speed of sound Community Noise Sources and Criteria Sound pressure Properties of Sound Waves Transportation noise Frequency Other internal combustion engines Wavelength Construction noise Zoning and siting considerations Characteristics of noise and Desibel scale Levels to protect Health and Welfare Frequency and Loudness Sound level and decibel scale Weighting networks Octave bands Rating systems

Noise Measurement – Measuring noise
Noise measurement equipment depends on the task to be performed For an initial survey – a sound level meter (SLM) is adequate for a rapid evaluation and identification of potential problem areas To study and also determine the characteristics of a noise problem area – an SLM, frequency analyzer and recorder are needed

Noise Measurement – Measuring noise
Sound Level Meter Used to measure the sound pressure level Available to cover a range of 20 to 180 dB Specifications refer to the American National Standards Institute (ANSI) – referred as “Specifications for Sound Level Maters (ANSI S ) Weighting networks of A, B, C are provided – total loudness level for a particular situation with consideration of the sound frequency, intensity and impact levels. Weighting network A – most commonly used: discriminates against frequency below 500 Hz – encompasses the most sensitive hearing range. Measuring environmental noise should be supplemented by the time/duration to determine the total quantity of sound affecting people

Noise Measurement – Measuring noise
Sound Level Meter (cont’d) Types of SLM: SLM provides setting for “F” (fast time response) and “S” (slow time response) Calibration by calibrator – generates a known decibel standard for QA/QC SLM Type Intended Use laboratory reference standard 1 for laboratory use, and for field use where the acoustical environment has to be closely specified and controlled 2 suitable for general field applications 3 primarily for field noise survey applications

Noise Measurement – Measuring noise
Noise Dosimeter Measure the amount of potentially injurious noise to which an individual is exposed over a period of time Can be set to the desired level – total up the exposure time to noise above the set level Does not identify the noise sources To determine the noise exposure and culpability – dosimeter should be coupled with a frequency analyzer/ human observer to record noise source identities

Noise Measurement – Measuring noise
Noise Dosimeter (cont’d) – Interpretation of results To calculate the noise exposure level of an employee working shifts of more or less than eight hours, it is necessary to normalise the employee’s exposure to an equivalent eight hour exposure (LAeq,8h). where: LAeq equals the equivalent continuous A-weighted sound pressure level occurring over the measured time; and T represents the shift length in hours (not to be confused with the sampling time). For shifts between 10 to 12 hours, add 1 dBA – extended shift In addition, shifts of 10 hours or more require adjustments to LAeq,8h values, as indicated in Table 3.1.

Noise Measurement – Measuring noise
Table 3.1 Correction factors for computing LAeq,8h from LAeq records

Noise Measurement – Measuring noise
Example 3.1 A personal noise dosimeter is placed on an employee for a representative period of six hours. At the end of the six hours, the LAeq reading is 93 dB(A). The employee works a 10 hour shift.

Noise Measurement – Measuring noise
Sound Analyzer Frequency analyzer – measure complex sound and sound pressure according to frequency distribution. Supplemented with SLM Covers different frequency bands Example: octave band analyzer, impact noise analyzer (peak level and duration of impact noise)

Noise Measurement – Measuring noise
Cathode-Ray Oscillograph Observing the wave form of a noise and pattern Magnetic tape recorder makes possible the collection of noise information in the field and subsequent analysis of the data in the office or laboratory

Noise Measurement – Measuring noise
Table 3.2: Background noise correction factor Background Noise Noise in the absence of the sound being measured that may contribute to and obscure the measured sound Correction can be made through subtraction method or application of correction factors (CF) as in Table 3.2 ΔL, dB AΔ, dB 1.0 6.9 1.5 5.3 2.0 4.3 2.5 3.6 3.0 3.5 2.6 ΔL, dB AΔ, dB 6.5 1.1 7.0 1.0 7.5 0.9 8.0 0.7 9.0 0.6 10 0.5 12 0.3 14 0.2 16 0.1 18 20 0.0 4.0 2.2 4.5 1.9 5.0 1.7 5.5 1.4 6.0 1.3

Noise Measurement – Measuring noise
Example 3.2 The measured overall sound pressure level around a fan is 83 dB. The measured overall sound pressure level for the background (ambient) noise in the room where the fan is located is 77 dB. Determine the overall sound pressure level produced by the fan alone.

Noise Measurement – Measuring noise
Added problem The experimental data shown below were measured around an air vent. The readings are the octave band sound pressure levels with the air flow stopped (background noise) and with the air flowing (data). Determine the octave band sound pressure levels and overall sound pressure level for the vent noise alone Octave band center frequency, Hz 63 125 250 500 1000 2000 4000 8000 Background LP, dB 79.0 76.1 73.6 70.7 68.1 66.0 64.3 63.0 Data LP, dB 79.1 76.6 76.3 78.7 81.2 83.1 78.1

Community Noise Sources and Criteria
Estimation of Community Reaction If noise spectrum data are not available, the LDN of the background noise, with suitable correctors may be used to estimate the anticipated community response to the environmental noise: The correction made to measured Ldn accounted for the effect of annoyance due to several influencing factors (presented in Table 4.1) such as below: Nighttime Location Time of the year Previous noise exposure Average community reaction to noise based on Ldn is given in Table 4.2.

Community Noise Sources and Criteria
Estimation of Community Reaction – Table 4.1. Correctors to be Added to the Measured Day-Night Level for Various Influencing Factors for Community Noise Reactionb Influencing Factor Description of condition CFdn, dBA Noise Spectrum Pure tones or impulsive noise present +5 No pure tone or impulsive sounds Type of location Quiet suburban or rural community +10 Normal suburban community Urban residential community Noisy urban residential community -5 Very noisy urban community -10 Time of year Summer or year-round Winter only or windows always closed Previous noise exposure No prior experience with the intruding noise Some prior experience with the noise or where the community is aware that good-faith efforts are being made to control noise Considerable experience with the noise and the group associated with the source of noise has good community relations Aware that the noise source is necessary, of limited duration, and/or an emergency situation bOnly one correction factor should be used from each category

Community Noise Sources and Criteria
Estimation of Community Reaction – Table 4.2. Average Community Reaction to Noise Based on the Day-Night Level, (Ldn) Corrected day-night level Ldn(corrected) Expected community response <62 dBA (dn) No reaction dBA (dn) Complaints dBA (dn) Threats of community action >72 dBA (dn) Vigorous community action

Community Noise Sources and Criteria
Example 4.1 The noise levels in a suburban area are given in Table 4.3. The area has had some prior experience with intrusive noises. There are no pure tone components of the noise, and it is not impulsive. The noise source will be present year-round. Determine the anticipated community response to the noise source. Duration A-weighted level Daytime 4 hours 60 dBA 6 hours 55 dBA 5 hours 50 dBA Nighttime 2 hours 45 dBA 7 hours 40 dBA

Community Noise Sources and Criteria – Transportation noise
Aircraft Noise The noise spectra of a wide fan jet (i.e. Boeing 747) reveal that sound pressure levels are higher on takeoff compared to landing Smaller aircraft have lower sound pressure levels (except for turbojets) Highway Vehicle Noise Predominant source of most automobiles during normal operation below about 55 km/h is the exhaust noise At speed 80 km/h, tire noise is dominant source. For truck, at speed more than 80 km/h tire noise is dominant – the noisiest is “cross-bar” tread Diesel trucks are 8 to 10 dB noisier than gasoline-powered For motorcycle, dominant source of noise is exhaust – highly dependent on the speed The U.S. Federal Highway Administration (FHA) has developed standards shown in Table 4.3

Community Noise Sources and Criteria – Transportation noise
Table 4.3. FHA noise standards for new construction a Either Leq or L10 may be used, but not both. The levels are to be based on a 1-hour sample Land Use Category Exterior design noise level dBAa Description of land use category Leq L10 A 57 60 Tracts of land in which serenity and quiet are of extraordinary significance and serve an important public need, and where the preservation of those qualities is essential if the area is to continue to serve its intended purpose. For example, such areas could include amphitheaters, particular parks or portions of parks, or open spaces, which are dedicated or recognized by appropriate local officials for activities requiring special qualities of serenity and quiet B 67 70 Residences, motels, hotels, public meeting rooms, schools, churches, libraries, hospitals, picnic areas, recreation areas, playgrounds, active sports areas, and parks C 72 75 Developed lands, properties, or activities, not included in categories A and B above D Unlimited Undeveloped lands E 52 (interior) 55 (interior) Public meeting rooms, school, churches, libraries, hospitals and other such public buildings

Community Noise Sources and Criteria – Other internal combustion engines
These devices as listed in Table 4.4 are not significant to average residential noise levels in urban area However the relative annoyance of most of the equipment tends to be high – U.S. EPA, 1971 The 8-hour exposure level is in reference to the equipment operator Table 4.4. Summary of noise characteristics of internal combustion engines

Community Noise Sources and Criteria – Construction noise
Table 4.5. Range of sound levels from various type of construction equipment (based on limited available data samples. (Source: U. S. EPA, 1972) 19 common types of construction equipment – range of sound levels as in Table 4.5. Annoyance resulting from construction noise: Single house construction in suburban communities will generate sporadic complaints if the boundary line 8-hour Leq exceeds 70 dBA Major excavation and construction in a normal suburban community will generate threats of legal action if the boundary line 8-hour Leq exceeds 85 dBA

Community Noise Sources and Criteria – Zoning and siting considerations
The U.S. Dept. of Housing and Urban Development (HUD) was charged with developing guides for zoning modifications or for siting of dwellings Annoyance for a specific noise exposure depended on both the average level of the noise and on the variability of the source of noise (Griffiths and Langdon, 1968) Table 4.6 list out criteria for new residential construction by HUD General external exposures Assessment Exceeds 89 dBA 60 minutes per 24 hours Unacceptable Exceeds 75 dBA 8 hours per 24 hours Exceeds 65 dBA 8 hours per 24 hours Discretionary: normally unacceptable Loud repititive sounds on site Does not exceed 65 dBA more than 8 hours per 24 hours Discretionary: normally acceptable Does not exceed 45 dBA more than 30 minutes per 24 hours Acceptable

Community Noise Sources and Criteria – Levels to protect Health and Welfare
Noise criteria levels that is necessary to protect the health and welfare of U.S. citizens listed in Table 4.7